The present invention relates generally to structural composites and more specifically to moldable pellets consisting of a combination of thermoplastic polymers and synthetic cellulosic fibers that may be made into structural composites.
Structural composites are well known and are used in a wide variety of applications that require plastic parts having a minimum threshold of mechanical properties such as strength and impact resistance while imparting cost savings in terms of manufacturing techniques and in terms of weight reduction. Examples of structural composites include sheet molding compound (SMC), fiber reinforced thermoplastics and structural reinforced injection molding (SRIM).
Introducing glass fiber or other reinforcing material into a thermoplastic or thermosetting polymer material typically makes structural composites. The glass fiber and polymer material may be mixed together and formed into a composite part in a wide variety of methods, including compression molding and injection molding. Structural composites made of glass fiber or other reinforcing material offer generally good mechanical properties in terms of impact, toughness, strength and may be used in a wide variety of applications.
One problem with glass reinforced or carbon fiber reinforced composites is that the reinforcement fibers are generally abrasive. This abrasiveness can adversely affect equipment used to mold the composite parts. This in turn increases the cost for manufacturing reinforced composites parts due to increased mold turnover and downtime associated with mold turnover.
Another problem with glass reinforced or carbon fiber reinforced composites is that the fiber tends to break during injection molding and extrusion compression molding processing. Thus, recycled parts made of reinforced composites lose significant mechanical properties associated with fiber length within the composite material during processing. Impact resistance is, in most cases, the most significantly affected mechanical property. However, strength and modulus may suffer as well.
Further, composite parts cannot be recycled without further degrading fibers within the composite material. Therefore, composite parts not made to exact specifications are disposed of as waste.
It is thus an object of the present invention to reduce abrasiveness in fiber reinforced structural composites without adversely affecting mechanical properties of the finished structural part.
It is another object of the present invention to process and recycle composite components without significantly reducing fiber length or compromising mechanical performance.
It is a further object of the present invention to reduce complexity in forming composite parts associated with traditional injection molding and compression molding techniques.
The above objects are accomplished by producing a moldable pellet consisting of a thermoplastic polymer or polymers, with or without fillers and additives, and a synthetic cellulosic fiber such as Rayon or Lyocell. The concentration of cellulose fiber within the pellet may vary from approximately 2-38 percent by weight or higher. This moldable pellet is suitable for molding in current molding applications such as, but not limited to, injection molding and extrusion compression molding.
It has been discovered that the impact performance of thermoplastics reinforced with synthetic cellulose fibers is excellent, typically superior to glass, carbon, natural fiber, or talc-reinforced thermoplastics and competitive with several impact resistant polymers such as ABS (acrylonitrile-butadiene-styrene), PC (polycarbonate)-ABS, Dylark, and other high impact polymers. In addition, synthetic fibers are non-abrasive and therefore will produce minimal wear on molding equipment. Also, because synthetic fibers are inherently tough, composite components may be processed and recycled without significantly reducing fiber length or compromising mechanical performance.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.